Hydrogen Peroxide Formation in Aqueous Solutions under UV-C Radiation

Article abstract of DOI:10.1134/S0018143918030128

The formation of hydrogen peroxide in bidistilled water under the influence of UV-C radiation from a DKB-9 low-pressure mercury lamp has been studied. The yield of hydrogen peroxide was (1 ± 0.2) × 10^?7 mol (L s)^?1. The wavelengths of radiation under the influence of which the formation of H₂O₂ is possible have been estimated. It has been assumed that the intermediate product of the reaction is the HO₂^./O₂^.-radical. To identify it, oxidation–reduction reactions in aqueous solutions containing Fe²⁺, Fe³⁺, and I^? ions at pH values from 0.8 to 8.1 have been studied. The quantum yield of HO₂^. radicals in an acidic medium under the influence of radiation from the mercury lamp is 0.015 ± 0.005.

Full text of DOI:10.1134/S0018143918030128

ISSN 0018-1439, High Energy Chemistry, 2018, Vol. 52, No. 3, pp. 212–216. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © I.M. Piskarev, 2018, published in Khimiya Vysokikh Energii, 2018, Vol. 52, No. 3, pp. 194–198.
PHOTOCHEMISTRY
Hydrogen Peroxide Formation in Aqueous Solutions
under UV-C Radiation
I. M. Piskarev
Skobeltsyn Research Institute of Nuclear Physics, Moscow State University, Moscow, 119234 Russia
e-mail: i.m.piskarev@gmail.com
Received July 31, 2017
Abstract⎯The formation of hydrogen peroxide in bidistilled water under the influence of UV-C radiation
from a DKB-9 low-pressure mercury lamp has been studied. The yield of hydrogen peroxide was (1 0.2) ×
10−7 mol (L s)−1. The wavelengths of radiation under the influence of which the formation of H2O2 is possible
i
HO2 Oi2−
have been estimated. It has been assumed that the intermediate product of the reaction is the
rad-
ical. To identify it, oxidation–reduction reactions in aqueous solutions containing Fe2+, Fe3+, and I− ions at
i
pH values from 0.8 to 8.1 have been studied. The quantum yield of
the influence of radiation from the mercury lamp is 0.015 0.005.
radicals in an acidic medium under
HO2
i
HO2 Oi2−
Keywords: hydrogen peroxide,
radical, Fe2+ and I− oxidation, UV-C radiation
DOI: 10.1134/S0018143918030128
INTRODUCTION
bulb. The treatment of a 20-mL sample of water with
solar radiation for 1 to 5 h resulted in the formation of
30 to 200 nmol (concentration from 1.5 × 10−6 up to
1 × 10−5 mol/L) of hydrogen peroxide. Illumination
with an electric bulb for the same time gave
8 to 16 nmol (concentration from 4 × 10−7 up to 8 ×
Mechanisms of the interaction of UV-C radiation
that can pass through air (200–280 nm) with the mat-
ter have been studied for a long time are well docu-
mented. There are monographs summarizing these
studies [1, 2]. One of the mechanisms is the direct
absorption of a photon by an energy level of a molecule
(provided that such a level exists) followed by the tran-
sition of the molecule to an excited state in which it
can undergo further transformations. If there is no
such energy level in the molecule, and dissolved oxy-
gen is present in the water, then reactions of type I and
II with a sensitizer in the triplet state are possible. Any
i −
10−7 mol/L) of hydrogen peroxide. The participation
i
HO2 Oi2−
of
radicals in this process was shown.
i
HO2 Oi2−
In [8, 9], it was shown that
radicals can
be formed in water by the action of UV-C radiation.
The radicals are in the following equilibrium:
i −
HOi2
O2
↔
+ H+, pKa = 4.8.
(1)
impurity in water can act as a sensitizer. The
radi-
O2
cal ion is formed in type I reaction, the reaction of
Depending on the acidity of the medium, the radi-
type II generates singlet oxygen [3].
i
cal exists in different forms. In [9], the yield of
on
HO2
In natural waters, there are always substances that
can play the role of a sensitizer; therefore, hydrogen
peroxide is formed in natural water under the influ-
ence of visible and UV radiation [4, 5]. In the case of
UV-C radiation with λ < 246 nm, the decomposition
of water molecules with the formation of hydroxyl rad-
icals is feasible in the absence of sensitizers in water.
However, the probability of this process is low [6].
Hydroxyl radicals are formed with a noticeable proba-
bility under the influence of vacuum ultraviolet at λ <
180 nm.
a beam of pulse and continuous UV-C radiation in an
i
acidic medium was estimated. The interaction of
HO2
radicals with one another should lead to the formation
of hydrogen peroxide. However, hydrogen peroxide
was not detected in [8, 9].
i
HO2 Oi2−
The formation of
radicals can be consid-
ered as a new mechanism of the interaction of photons
of visible and ultraviolet ranges with aqueous solu-
tions. Therefore, it is of interest to obtain information
i
HO2 Oi2−
on the formation of
radicals under the influ-
Gudkov et al. [7] studied the formation of hydro-
gen peroxide in bidistilled water under the influence of ence of UV-C radiation in pure water and in aqueous
sunlight and artificial illumination with an electric solutions of substances that cannot exist in the triplet
212

HYDROGEN PEROXIDE FORMATION IN AQUEOUS SOLUTIONS
213
state, do not enter type I and II reactions at any rate, acid. To a 5 mL sample of treated water, 0.1 mL of tita-
and are barely capable of the direct absorption of pho-
tons.
The purpose of this work is to determine the yield
of hydrogen peroxide in bidistilled water and the gen-
nium trichloride solution was added. Titanium tri-
chloride forms a complex with hydrogen peroxide hav-
ing a maximum in the absorption spectrum at λ =
410 nm [11]. The method was calibrated using hydro-
gen peroxide solutions of a known concentration, to
which TiCl3 was added.
i
HO2 Oi2−
eration rate of
radicals in aqueous solutions
under the influence of UV-C radiation and to assess
the possible mechanism of the formation of
i
HO2 Oi2−
The redox properties that allow the products, gen-
erated in an aqueous solution by UV irradiation, to be
radicals.
i
HO2 Oi2−
identified as
radicals have been investigated
using several detection systems.
EXPERIMENTAL
To determine the divalent iron oxidation rate, a
solution of Mohr’s salt with a concentration from 2 to
50 g/L in 0.4 M sulfuric acid, pH 0.8 was used. The
concentration of trivalent iron in Mohr’s salt caused
by the spontaneous oxidation of ferrous ion during
storage of the reagent did not exceed 0.5%. The treat-
ment time of Mohr’s salt solution with UV-C radia-
tion was 1 and 2 min.
An OUFb-04 ultraviolet bactericidal irradiator with a
9-W ozone-free, low-pressure DKB-9 mercury lamp
with a housing made of uviol glass was the radiation
source. The lamp operates continuously, gives mono-
chromatic radiation with a wavelength of 253.7 nm. The
photon flux according to the manufacturer’s certificate
data was I0 = 5.4 × 10−8 mol (cm2 s)−1 at a distance of
3 cm from the surface of the lamp. The average lifetime of
the lamp is 6000 h, but the average operating time is
1000 h due to contaminations of the inner surface of the
glass. Therefore, the actual intensity was measured before
the experiments and after the entire set of experiments.
To determine the radiation intensity of the lamp,
the yield of the decomposition of hydrogen peroxide
samples was measured. The concentration of hydro-
gen peroxide was 0.01 mol/L, pH 3.8. The acidic pH
of the solution is due to the peroxide stabilizer. The
treatment of peroxide with lamp radiation was carried
out in a glass beaker with a diameter of 40 mm and a
depth of 60 mm. The concentration of peroxide in the
initial and treated solution was determined by titrating
the entire volume of the treated sample with 0.05 N
potassium permanganate solution in an acidic
medium at a temperature of 80°С. It was found that
the thickness of the total absorption layer was 55 mm.
For the total absorption layer, the concentration
dependence of the peroxide remained after irradiation
with the mercury lamp for 5 to 30 min was determined.
The distance from the surface of the liquid to the lamp
was 30 mm.
To estimate the rate of reduction of trivalent iron,
an aqueous solution of iron nitrate Fe(NO3)3 ⋅ 9H2O
with a concentration of 0.04 g/L, pH 3.4 was used.
In both cases, the concentration of trivalent iron
Fe3+, which was in the initial solution and accumu-
lated during oxidation of divalent iron in Mohr’s
salt, was determined from the 304-nm band in the
absorption spectrum (molar absorption coefficient
ε = 2100 L (mol cm)−1) [12].
Oxidation of iodide ions. An aqueous solution of
KI with a concentration of 5 g/L was used. The initial
acidity value was 5.6. The measurements were per-
formed at pH values from 1.4 to 8.1. The pH was set by
introducing sulfuric acid and alkali NaOH into the
stock solution. The volume of the acid or alkali did not
exceed 2% of the volume of the prepared solution.
When iodide ions are oxidized, triiodide ions are
formed. The concentration of triiodide was deter-
mined from the absorbance of the UV band at λ =
288 nm, ε = 2.65 × 104 L (mol cm)−1 [13].
In order to determine the radiation intensity of the
lamp from these data, a decrease in the concentration
of peroxide under irradiation was calculated in terms
of the known mechanism [10]. The calculation was
performed using the MathCad package 14. The emis-
sion intensity of the lamp was set as a parameter.
The detecting solutions were exposed to the radia-
tion of the mercury lamp in Petri dishes with a diame-
ter of 40 mm. The volume of the treated liquid in all
the experiments was 5 mL, the thickness of the liquid
layer was 7 mm. The distance from the surface of the
liquid to the surface of the lamp is 30 mm.
The yield of hydrogen peroxide generated by UV
radiation from the mercury lamp in pure bidistilled
water was measured. To this end, water of 5 mL in vol-
ume was irradiated in a Petri dish for 5 h. The distance
from the surface of the liquid to the lamp was 30 mm.
The pH was measured with an EKONICS Expert-001
instrument (Russia). The UV absorption spectra were
recorded with an AKVILON SF-102 spectrophotometer
(Russia) operating wavelength range 200−1100 nm. The
To identify the peroxide, freshly prepared TiCl3 solu- optical path length of the cell was 10 mm. We used
reagent grade chemicals and bidistilled water with pH
5.5. To process the experimental results, the MathCad
tion was added into the irradiated water sample. Tita-
nium trichloride was prepared by dissolving 0.3 g of
titanium metal in 50 mL of concentrated hydrochloric 14 software package was used.
HIGH ENERGY CHEMISTRY Vol. 52 No. 3 2018

214
PISKAREV
RESULTS
A
0.3
Determination of DKB-9 Mercury Lamp
Radiation Intensity
Let us estimate the possibility of decomposition of
hydrogen peroxide used as a radiation detector under
the action of radicals. If the radical is
0.2
0.1
0
HOi2 Oi2−
i
formed, it exists predominantly in the form of
,
HO2
3
since its pKa is value 4.8 and the hydrogen peroxide
solution used in the work has pH 3.8. The reaction
with hydrogen peroxide is as follows:
1
2
300
350
400
450
500
nm
250
i
i
H O +
→ H O +
.
(2)
HO2
HO2
2
2
2
2
i
Neither hydrogen peroxide nor
radicals are
HO2
Fig. 1. Identification of hydrogen peroxide in a sample of
bidistilled water treated with mercury lamp UV radiation;
(1) pure hydrogen peroxide solution with a concentration
of 0.01%; (2) water sample treated with UV radiation for
5 h; (3) a sample treated for 5 h after the addition of 0.1 mL
consumed in this reaction, only the transfer of hydro-
gen atoms takes place. The formation of hydroxyl rad-
icals in water by the action of radiation with λ =
253.7 nm is impossible. Therefore, the mechanism of
decomposition of peroxide can only be the direct
absorption of photons by hydrogen peroxide mole-
cules followed by their degradation. The initial con-
of TiCl .
3
+
gives rise to other compounds. The formation of
ions was identified in [8].
NH4
centration of peroxide was (0.01
0.0005) mol/L
to become [H2O2] = (0.0032 0.0004) mol/L after
30-min irradiation. Calculation reported in [10]
describes the experimental data at an intensity of I0 =
Oxidation of Divalent Iron
(5.7 0.5) 10−8 mol (cm2 s)−1. At the end of the set of
experiments, the intensity decreased by 10%. Such a
reduction lies within the errors of all measurements, so
it could be ignored.
Figure 2 shows the dependence of the concentra-
tion of ferric ion formed in an acidic solution of
Mohr’s salt under the influence of mercury lamp radi-
ation per 1 min, on the concentration of ferrous ion.
Oxidation of iron can be due to the interaction with
HOi2
Formation of Hydrogen Peroxide
. With increasing treatment time to 2 min, the
Fe3+ concentration increases proportionally. The con-
centration of Fe3+ increases with increasing Fe2+ con-
centration and reaches a maximum at [Fe2+] = 40–
50 g/L (100–130 mmol/L). The maximum concen-
i
In [8], we observed the generation of
radicals
HO2
under the influence of UV-C radiation. The interac-
i
tion of
radicals should lead to the formation of
HO2
H2O2. Figure 1 shows the absorption spectrum of a
solution of pure hydrogen peroxide, the absorption
spectrum of a sample of bidistilled water immediately
after irradiation with a mercury lamp for 5 h, and the
spectrum of the same irradiated sample after the addi-
tion of titanium trichloride to it.
tration of trivalent iron formed is [Fe3+] = 195
10 μmol/L. Such a character of the dependence can be
i
due to the decay of radiation-induced
radicals in
HO2
the solution in the reaction with one another at low
ferrous ion concentrations [14]. As a result, the yield of
oxidized iron turns out to be lower at low Fe2+ concen-
Figure 1 (curve 3) shows the appearance of a peak
at 410 nm characteristic of the hydrogen peroxide
complex with TiCl3. Based on this spectrum, the con-
centration of hydrogen peroxide in the sample of water
treated for 5 h was found to be [H2O2] = (0.006
trations and reaches a plateau at high Fe2+ concentra-
tions. Therefore, based on the maximum concentra-
tion of the ferric ions formed, we can estimate the yield
i
of
radicals. The interaction of divalent iron in an
HO2
0.001)% or 2 × 10−3 mol/L. Hence, the yield of
hydrogen peroxide generated by radiation from of the
DKB-9 lamp is (1 0.2) 10−7 mol (L s)−1.
i
acidic medium with
reactions:
radicals is described by the
HO2
Fe2+ + HO2i + H+ → Fe3+ + H2O2,
The absorbance in the range 250–400 nm of water
exposed to UV radiation for 5 h (Fig. 1, curve 2) is
much larger than that the solution of pure hydrogen
peroxide (Fig. 1, curve 1), although the concentration
of pure peroxide in the sample is greater according to
curve 1. This means that irradiation with the UV lamp
(3)
(4)
−1
k = 1.5 ×106 L mol s
,
(
)
3
Fe2+ + H2O2 → Fe3+ + OHi + OH−,
−1
k = 56 L mol s
,
(
)
4
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HYDROGEN PEROXIDE FORMATION IN AQUEOUS SOLUTIONS
215
[I3–], µmol/L
[Fe3+], µmol/L
150
250
200
150
100
50
100
50
0
0
50
100
150
1
3
5
7
9
pH
[Fe2+], mmol/L
Fig. 2. Dependence of the concentration of ferric ion
Fig. 3. Dependence of the concentration of triiodide [ −],
3+
I3
[Fe ], μmol/L, formed by irradiation with light from a
μmol/L, formed by irradiation with light from a mercury
lamp for 1 minute in KI solution, on the pH of the aqueous
solution.
mercury lamp for 1 minute in an acidic solution of trivalent
2+
iron, on the concentration of [Fe ], mmol/L.
Fe2+ + OHi → Fe3+ + OH−,
i
in an acidic medium. The reaction of
radicals
HO2
(5)
(6)
−1
k = 109 L mol s
,
with trivalent iron in an acidic medium is impossible.
(
)
5
HOi2 + HO2i → H2O2 + O2,
Oxidation of Iodide Ions
−1
k = 9.6 ×108 L mol s
.
(
)
6
The dependence of the concentration of triiodide
formed in a KI solution during 1-min irradiation with
the mercury lamp is shown in Fig. 3. At pH values
from 1.4 to 1.9, the triiodide concentration does not
change within the limits of error, it is maximal, making
−
Hereinafter, data on the reaction rate constants
from the reference book [15] were used. It can be seen
from reactions (3)–(6) that three trivalent iron ions
i
are formed per one primary
radical. In this case,
HO2
134 13 μmol/L. The concentration of decreases
I3
we neglect the consumption of the hydrogen peroxide
generated by the primary UV-C radiation. Based on
rapidly with increasing pH, at pH 4.4 the decrease
−
the saturation concentration [Fe3+] = 195
slows down considerably, and the concentration of
I3
i
remains almost unchanged starting from pH 6.1. Qual-
itatively, the character of the dependence is caused by
the fact that the value of the dissociation constant for
i
10 μmol/L, the
generation rate in water is (1.08
HO2
0.1) × 10−6 mol (L s)−1. The rate of generation of the
radicals in a 5 mL Petri dish with a surface of 7 cm2 is
(7.7 0.8) × 10−10 mol (cm2 s)−1.
HO2 Oi2−
the
radical is pKa = 4.8. In a strongly acidic
i
medium, it exists as
, which oxidizes iodide ions;
HO2
The reduction of the trivalent iron built-up during
irradiation under the conditions of the present work
(acidic medium) is impossible. This conclusion is
confirmed by the experimental data obtained in this
study.
at pH > 6, it exists predominantly in the reductant
form of i −, and oxidation of iodide ions becomes
O2
impossible.
DISCUSSION
Reduction of Trivalent Iron
A possible mechanism for the formation of oxi-
dants could be the process H2O → OH• + H•. The
dissociation energy of the water molecule is
499 kJ/mol [16]. This corresponds to a quantum
energy of 5.03 eV or a wavelength of λ ~ 246 nm.
Therefore, hydroxyl radicals cannot be generated by
ultraviolet radiation with λ = 253.7 nm of the lamp. In
[8], the experimental results were explained by the for-
i
No reduction of ferric ions in a Fe(NO3)3 ⋅ 9H2O
solution was detected. In the case of UV-C irradiation
of the solution, only an increase in the absorbance at
304 nm due to trivalent iron was observed. The effect
may be explained in terms of the fact that during the
storage of Fe(NO3)3 ⋅ 9H2O, trivalent iron had been
partially reduced to divalent iron, which underwent
oxidation in this experiment. The absence of reduc-
tion of trivalent iron means that species with reducing
mation of
radicals by the action of UV radiation.
properties are not produced by the action of radiation A mechanism was proposed for the formation of HO2i
HO2
HIGH ENERGY CHEMISTRY Vol. 52 No. 3 2018

216
PISKAREV
The acidity of methemoglobin solution is pH 7.4.
radicals by pulsed UV-C irradiation in an acidic
medium through excited states of water molecules [9].
i
HO2 Oi2−
In such a medium,
radical exists in the form
H2O + hν → H2O*.
(7)
of the negative radical ion i −, which can freely inter-
O2
act with the positive Fe3+ ion.
The linear decadic absorption coefficient of water
is ~0.8 m−1 at λ = 200 nm, it reaches a minimum ~2 ×
10−2 m−1 at λ ~ 470 nm, and then almost monotoni-
cally increases with increasing wavelength up to
~20 m−1 at λ = 970 nm [17]. Absorption for the peak at
λ = 970 nm is measured directly using an SF-102
spectrophotometer, the molar absorption coefficient
is ε = (3.1 0.1) × 10−3 L (mol cm)−1. Excited at wave-
lengths of 200–1200 nm are vibrational and electronic
levels of water molecules [7] whose energy is insuffi-
cient for changing the structure of the molecule, so
they can serve only as an energy storage.
CONCLUSIONS
The results of the study suggest the existence of a
mechanism for the effect of UV-C radiation on aque-
i
HO2 Oi2−
ous solutions through the formation of
icals.
rad-
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2. Rohatgi-Mukherjee, K.K., Fundamentals of Photo-
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H2O* + H2O → H2O2 + H2.
(8)
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(9)
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in terms of energy. The standard enthalpy of the for-
mation of liquid water at 298 К is −285.8 8 kJ/mol,
that of hydrogen peroxide is −187.8 kJ/mol, and the
enthalpies of formation for the simple substances H2
and O2 are conventionally taken to be zero [16]. Reac-
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i
HO2 Oi2−
radicals. The oxidation of Fe2+
14. Piskarev, I.M., Zh. Tekh. Fiz., 1999, vol. 69, no. 1,
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and I− in an acidic medium and the nonoccurrence of
p. 58.
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i
possibility. The quantum yield of
radicals in an
HO2
acidic medium in the case of continuous irradiation
16. Luo, Yu-Ran., Handbook of Bond Dissociation Energies
with a light beam at λ = 253.7 nm is 0.015 0.005.
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Translated by V. Makhaev
reduction to deoxyhemoglobin has been observed:
i −
Hb(Fe3+) +
→ Hb(Fe2+) + O2.
(10)
O2
HIGH ENERGY CHEMISTRY
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2018